DEC Rainbow / Pro video on VGA monitors?

[Warner Losh]

As a PS, I connected the real vr201 with a keyboard and got the attached
photo. It looks like there is a one line error about missing keyboard in
the first line when there is no keyboard. Counting out the rows on the boot
screen confirms. So this is much closer than I thought.

Warner



On Sun, Jan 20, 2019, 3:16 PM Warner Losh <imp at bsdimp.com wrote:

>
>
> On Sun, Jan 20, 2019 at 12:57 PM Marvin Johnston via cctalk <
> cctalk at classiccmp.org> wrote:
>
>>
>> > I'm trying to find a way to get my DEC Rainbow's monochrome output onto
>> a
>> > newer monitor than my aging VR201 (especially since I zapped something
>> in
>> > it and my diagnostic efforts to date haven't fixed it).
>>
>> I can't remember the video output on the Rainbow, but I wanted to do
>> something similar to have one setup for the S-100 machines. After
>> looking on eBay (before I banned them from my use), I found a device
>> that basically had RCA audio/video inputs with a VGA output. It also had
>> the advantage of having an analog TV tuner built in so I could also use
>> things like the old video games that had the Channel 3/4 output.
>>
>> The device is buried somewhere so I can't tell you the brand.
>>
>
> Yea. I'm going to order one or two others to see if I can get them to
> work... The TRB says:
>
> 4.4.8.14 Composite Video Signal Characteristics
> The composite video output provides a compatible EIA RS-170 output
> generated by combining the video signal with a composite sync signal.
>
> NOTE The use of dc coupling is not in strict agreement with the EIA RS-170
> standard. To agree with RS170, the video generator output load would
> require a 10 microfarad capacitor in series with the output. Without the
> capacitor, the RS-170 2 milliamp dc short circuit requirement is violated.
>
> The composite video output has the following nominal characteristics:
> I. Output impedance = 75 ohms, dc coupled to 0.0 V
> 2. Sync level = 0.0 V
> 3. Reference black level = approximately 0.3 V with a 75 ohm load
> 4. Reference white level = approximately 1.0 V with a 75 ohm load
> 5. The composite sync waveform conforms to EIA RS-170 standards.
>
> The vertical interval is composed of six equalizing pulses, six vertical
> sync pulses, and six more equalizing pulses.
>
> The timing is as follows:
> Equalizing pulse width = 2.33us +/- 50ns
> Vertical pulse width = 27.28us +/- 200ns
> Horizontal pulse width = 4.71us +/- 50ns
> Horizontal blank width = 11.84us +/- 50ns (80-column mode)
>  = 12.34us +/- 50ns (132-column mode)
> Front porch 1.54us +/- 50ns
>
> This differs a little from what I've found online for RS-170 timings:
>
> Reference Black = 0.075V
> White = 1.00V
> Sync = -0.40V
>
> in some places but seems to correspond to the pics at
> https://en.wikipedia.org/wiki/Composite_video almost exactly. So I'm
> confused.
>
> But I've seen other numbers as well. And the timings are roughly
> consistent with the envelops suggested in an old terribly scanned doc from
> the 80's that talks about video formats...
>
> Anyway, video formats always proliferate into a cluster of almost the same
> standards and it's hard to know what, exactly, to call them...
>
> I'm not sure if this helped, or not :(
>
> Warner
>